1. Field of the Invention
The present invention relates to a drive assembly for a vehicle having an overload coupling between a drive shaft and a driving pinion to limit the transmission of excessive and damaging torques through the drive assembly. The overload coupling includes an overload clutch.
2. Description of Related Art
Various manual transmissions for internal combustion engine driven vehicles are known in the art. In a typical arrangement, an internal combustion engine provides a driving force to drive a drive shaft through suitable engine gearing (i.e., drive assembly). This can be accomplished by a belt-driven constant velocity transmission (“CVT”) that acts, preferably through a manual transmission, on a driven shaft that is connected to at least one driving wheel. A forward gear, a reverse gear, or neutral positions can be selected as desired by the manual transmission.
In known drive assemblies, a centrifugal clutch and a CVT provide variable transmission ratios. The clutch and CVT are incorporated between the internal combustion engine and the toothed gearing of the drive assembly. The CVT drives the toothed gearing of the drive assembly and thus moves the vehicle. It is preferred that the driving assembly provide a plurality of speeds, for example, a fast forward gear, a slow forward gear and a reverse gear. One particular problem with this drive concept has been that, in particular when the transmission is subjected to large impact loads in the drive train, such as those that occur, for example, when the vehicle jumps, the gearing will fail or be damaged and possibly destroyed after a number of such load reversals. These load peaks in the drive assembly are caused in particular because the high moment of inertia of the CVT and the gear ratio of the toothed gearing of the drive assembly make the drive assembly particularly stiff so that it cannot attenuate the load peaks that occur. This leads to load peaks, in particular at the output of the drive assembly of the output shaft. These impact loads stem from the difference between the absolute speed of the motor vehicle that is jumping and the circumferential velocity of the wheels of the motor vehicle which, when they land after the jump, dig into the ground with almost no slip.
Conventional drive assemblies such as the one disclosed in U.S. Pat. No. 3,997,043 include an overload clutch disposed between the transmission and the wheel of the vehicle. The overload clutch disengages when a torque transmitted therethrough exceeds a predetermined value so that the overload torque does not damage the transmission. Such overload clutches must be large to withstand the relatively large torques that are generated in the gear train between the transmission and the wheels.